The present application claims priority from Japanese Patent Application Hei 11-232815 the disclosure of which is incorporated herein by reference.
1. Technical Field to Which the Invention Belongs
This invention relates to a novel DNA fragment which has the effect of remarkably enhancing the expression of a gene.
2. Prior Art
In recent years, molecular breeding using genetic engineering techniques has been intensively applied. However, a problem exists in using such techniques that in a case where a foreign gene is to be expressed in a plant the gene transferred into the plant is not always expressed at a sufficiently high level, and an expression is, in fact, lower than expected. In attempting to produce a substance in a plant, it is requisite to express a transferred gene at a high level. Accordingly, the development of techniques capable of achieving high gene expression is of prime importance.
One technique used for promoting the expression of foreign genes is the use of DNA fragments having a nucleotide sequence capable of promoting gene expression. Examples of these DNA fragments include 5xe2x80x2-untranslated leader sequences and intron sequences. For example, it has been reported that the expression of a foreign gene can be promoted by inserting the first exon (5xe2x80x2-untranslated leader sequence) of corn Shrunken-1 gene (Maas et al., Plant Mol. Biol. 16:199-207, 1991) or the first intron of castor bean catalase gene (JP (Kokai) HEI 3-103182) into the upstream of the foreign gene and then expressing the foreign gene. It has also been reported that some other 5xe2x80x2-untranslated leader sequences and intron sequences originating in plants promote gene expression (Koziel et al. Plant Mol. Biol. 32:393-405, 1996).
The effect of promoting gene expression of an intron sequence is affected by the length of the adjacent exon sequences. In the case of the sixth intron of corn alcohol dehydrogenase 1 gene, for example, a maximum effect is established when a 76 bp exon is located in the 5xe2x80x2-side adjacent to the intron and a 53 bp exon is located in the 3xe2x80x2-side adjacent thereto (Mascarenhas et al. Plant Mol. Biol. 15:913-920, 1990).
In addition, the amplification of gene expression by an intron is affected by various factors such as the promoter used, the plant species involved, and the nucleotide sequence of a structural gene (Koziel et al. Plant Mol. Biol. 32:393-405, 1996). It is to be noted that not every 5xe2x80x2-untranslated leader sequence or intron sequence promotes gene expression. Accordingly, it is strongly desired to further identify various types of 5xe2x80x2-untranslated leader sequences and intron sequences capable of sufficiently amplifying gene expression.
An object of the present invention is to provide a novel DNA fragment which is capable of remarkably enhancing gene expression.
Another object of the present invention is to provide a method of remarkably enhancing gene expression, in particular expression of a foreign gene, in a host by using the novel DNA fragment.